A fracture near a joint has always been difficult to treat, as the ideal treatment is to achieve rigid fixation of the fracture fragments while allowing nearly immediate motion of the joint.
In order to simplify the description the present invention is described in connection with fractures of the wrist, and particularly those fractures collectively referred to as Colles' fractures. A person skilled in the art will appreciate that the invention is also applicable in fixation of other bones. Possible other bones include, but are not limited to, the distal or lower end of the humerus, the lower tibia and the lower fibula. This requires a change of the shape of the device for each specific area, but the same principles are used irrespective of the site of the fracture. However, the major use of the invention is thought to be for fixation of Colles' fractures.
Treatment of distal radius fractures has been a problem, both because of the frequency of the injury as well as the difficulty in treating them. The goal of treatment is to restore joint congruity and anatomy, minimize the risk of arthritis, and maximize joint mobility. However, although these injuries are almost always treated on an outpatient basis, they typically result in stiffness, arthritis, and diminished function.
There are today essentially four general groups of options available for the treatment of Colles' fractures: (1) closed reduction and casting, (2) external fixation, (3) open reduction and internal fixation, and (4) percutaneous pinning and/or limited open pinning. Each method has its limitations; each has its benefits.
Closed reduction simply involves setting or aligning the broken bone manually and applying a cast to the arm. This treatment avoids any trauma associated with surgery, and is inexpensive. However, it has several disadvantages. It involves cast immobilization until healing of the bone fragments occurs; this frequently results in considerable stiffness. This stiffness is not just confined to the wrist and forearm. Immobilizing the arm in an elderly individual frequently also results in considerable stiffness to the fingers, elbow, and shoulder as well. In addition, this technique is very limited in its ability to hold all but the simplest, most stable fracture patterns in proper alignment. Unstable fractures commonly redisplace during healing, which can lead to arthritis and pain.
External fixation involves the application of relatively large diameter pins inserted into the finger metacarpals and into the radius above the fracture. These pin clusters are then connected with a bar or frame, essentially "bypassing" the fracture site. Typically, two pins are placed in the hand, and two pins in the radius. The frame may distract the wrist as well, in order to assist with fracture reduction, by using the soft tissue sleeve around the fracture to help squeeze the fragments into position. Although external fixation has its proponents, it has its problems. The wrist and hand are rigidly held by the frame, and the pins through the skin tend to irritate the tendons and cause scarring. These problems together cause considerable stiffness in both the wrist and the fingers; frequently the functional loss of grip can be more disabling than the fracture. Pin site infections may also occur and compromise results. External fixation may not achieve an anatomic reduction of the fragments. Currently, external fixation is used for more severely comminuted, fragmented fractures.
Open reduction involves making an incision over the wrist reducing the fragments, and applying plates, screws, and pins as needed. For the Colles' fracture open reduction and internal fixation is seldom used, for several reasons. First, the trauma associated with the dissection and exposure can lead to scarring of the tendons, loss of gliding, and stiffness. Second, the dissection can compromise the blood supply to the fragments, which can result in delayed unions and occasionally non-unions. Third, the fragments tend to be small and osteoporotic; drilling holes and placing screws frequently fragments these pieces further, making anatomic reduction even more difficult. Fourth, most of the fragments and displacement in the typical Colles' fracture are on the dorsal side, and the irregularity of the radius in this area together with the many tendons found near the bone on this side makes it undesirable to place plates and screws dorsally. Finally, these fractures are often comprised of numerous small pieces which must be reduced in a jigsaw puzzle type of arrangement, not easily treated by plate and screw fixation.
Percutaneous pinning involves the placement of small stiff pins, also called K-wires, across fragments of the fracture. The pins may be inserted directly through the skin while imaging the fracture with a fluoroscopy unit. Limited small incisions may also be used. Typically, pin diameters range from 0.035" to 0.062", with the 0.045" and 0.054" pin sizes commonly used in the U.S.A. Pinning has certain advantages. Using a percutaneous or limited open technique to pin fragments allows the fracture to be internally fixed. This provides some additional stability internally which is not available when the fracture is treated with a cast alone. The fragments in these fractures tend to be small and the bone osteoporotic. As a result, pins are more appropriate as a type of fixation than screws in this setting. A small diameter pin has less chance of weakening the fragment and comminuting it further compared with screw holes that are made with even small diameter bone screws.
Pinning, however, has its problems. In order to secure a fragment, there must be a stable bone nearby for securing the pin. Frequently, the only stable piece of bone is the proximal fragment, which may be some distance and at a difficult angle away from the fragment to be pinned. Since the pins have a small diameter, they are likely to bend or displace if the stable piece of bone is relatively far from the fracture fragment. This reduces the ability of the pin to maintain the position of the fragment and, in turn, impedes the process of healing.
In certain cases multiple fragments are put together like stacking cards, by fixing one fragment to a stable proximal piece, and then pinning a second fragment to the first piece, which is assumed to be stabilized by the first pin. This frequently makes the entire assembly dependent upon one or two pins which may engage the stable proximal cortex at some distance from the fracture fragment. Such situations are often unstable.
Another problem with pinning is that the stable piece of bone that the fragment is pinned to has to be located on the opposite cortex from where the pin is inserted. If the only nearby solid piece of bone is located on the cortex adjacent to the fracture fragment, pinning becomes a geometric impossibility. This situation occurs frequently when a dorsal ulnar fragment occurs. If the opposite volar radial surface is fractured in such cases as is often the case, there is no stable cortex available to the angles of pin insertion that are technically feasible.
Examples of these problems with pinning are often encountered in treatment of Colles' fractures involving a radial styloid fragment fixed by a percutaneous trans-styloid pin. The fracture is reduced, and the fluoroscopy unit is used to pass a pin through the radial styloid on an angle to engage the ulnar cortex proximal to the distal fragment. The ability of the pin to hold the radial styloid fracture fragment in an appropriate position is dependent upon the fixation of the pin in the stable proximal ulnar cortex. Since the distance to this fixation site is quite far, and because the small diameter of the pin permits bending, small angular deflections of the pin in its site of purchase at the proximal fragment may lead to significant displacements of the fractured radial styloid.
Because pins have a strong tendency to bend and displace due to motion of the joint, pins are hardly ever used without casting. This means that the patient is still subjected to the common complications of stiffness and loss of function that is associated with the cast.
Ideally the treatment of distal radius fractures should have the same goal as treatment of any other fracture near a joint, namely, achieving rigid fixation of the fracture fragments while allowing nearly immediate mobility of the joint. As can be seen from this discussion, none of the current methods of treatment achieves this goal. Pins alone do not provide adequate stability by themselves and still require a cast. External fixation allows rigid fixation, but does not allow direct reduction of the fracture site, and is associated with considerable morbidity from the complications of stiffness. Closed reduction may cause stiffness as well, and frequently fails to preserve anatomic reduction.
One primary objective of the present invention is to satisfy the goal of providing rigid fixation of fracture fragments while allowing immediate motion of a joint. This objective is satisfied using the technique disclosed in the characterizing clause of the independent claim which follows. The means according to the invention provides an implantable way of constraining by direct contact one or more pins which have been placed to secure fractured bone fragments.
Expedient embodiments of the present invention are disclosed in the dependent claims.